Publications
Microburst recognition performance of TDWR operational testbed
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather System, 30 January - 3 February 1989, pp. 25-30.
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Summary
This paper describes current work in assessing the microburst recognition performance of the Terminal Doppler Weather Radar (TDWR) operational testbed. The paper is divided into three main sections: microburst recognition algorithm, performance assessment methodology and results. The first section provides an overview of the prototype TDWR microburst recognition algorithm The algorithm uses radar data from both surface scans and scans aloft to identify microburst events. The surface scan is used to identify microburst outflows, and the scans aloft provide information concerning reflectivity and velocity structures associated with microbursts to improve recognition rate and timeliness. The second section of the paper describes the methodology for assessing the recognition performance of the system. The performance of the testbed system is addressed from two viewpoints: radar detectability and pattern recognition capability. The issue of radar detectability is examined by comparing radar and mesonet data to determine if any events observed by the mesonet fail to be observed by the radar. The issue of pattern recognition performance is assessed by comparing microburst recognition algorithm outputs with truth as determined by expert radar meteorologists. The final section of the paper provides performance results for data collected by the testbed radar at Huntsville, AL and Denver, CO.
Summary
This paper describes current work in assessing the microburst recognition performance of the Terminal Doppler Weather Radar (TDWR) operational testbed. The paper is divided into three main sections: microburst recognition algorithm, performance assessment methodology and results. The first section provides an overview of the prototype TDWR microburst recognition algorithm The...
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The FAA Terminal Doppler Weather (TDWR) Program
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather Systems, 30 January - 3 February 1989, pp. 414-419.
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Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in the terminal area and providing warnings that will help pilots successfully avoid it on approach and departure. Wind shear has caused more U.S. air-carrier fatalities than any other weather hazard. A 1983 National Research Council (NRC) study (National Research Council, 1983) identified low-altitude wind shear as the cause of 27 aircraft accidents and incidents between 1964 and 1982. A total of 488 people died in seven of these accidents, 112 of them in the 1975 crash of Eastern Flight 66 at New York and 153 in the crash of Pan American Flight 759 at New Orleans in 1982. Since the NRC study was completed, the National Transportation Safety Board (NTSB) has investigated at least three more wind-shear incidents. One of these, the crash of Delta Flight 191 at Dallas/Fort Worth on August 2, 1985, took another 137 lives. Wind shear is not a serious hazard for aircraft enroute between airports at normal cruising altitudes, but low-level wind shear in the terminal area can be deadly for an aircraft on approach or departure. The most hazardous form of wind shear is the microburst, an outflow of air from a small-scale but powerful downward gush of cold, heavy air that can occur beneath a thunderstorm or rain shower or even in rain-free air under a harmless-looking cumulus cloud. As this downdraft reaches the earth's surface, it spreads out horizontally, like a stream of water sprayed straight down on a concrete driveway from a garden hose. An aircraft that flies through a microburst at low altitude first encounters a strong headwind, then a downdraft, and finally a tailwind that produces a sharp reduction in airspeed and a sudden loss of lift. This deadly sequence of events caused the fatal crash at Dallas/Fort Worth in 1985, as well as a number of other serious air-carrier accidents. Wind shear can also be associated with gust fronts, warm and cold fronts, and strong winds near the ground. It is important for pilots to be trained in recovery techniques to use if they are caught in wind shear. But a sudden windspeed change of at least 40 to 50 knots, which is not uncommon in microbursts, presents a serious hazard to jet airliners, and some microbursts simply are non-survivable. The only sure way to survive wind shear in the terminal area is to avoid it. However, flight crews do not have adequate information available today to predict or detect wind shear. The primary goal of the IDWR program is to provide pilots with an objective, quantitative assessment of the wind-shear hazard. The TDWR system also will improve operational efficiency and reduce delays in the terminal area by providing air traffic control supervisors with timely warnings of impending wind shifts resulting from gust fronts.
Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in...
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Weather sensing with airport surveillance radars
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather System, 30 January - 3 February 1989, pp. 68-74.
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Modern airport surveillance radars (ASR) are coherent, pulsed-Doppler radars used for detection and tracking of aircraft in terminal area air space. The Federal Aviation Agency (FAA is procuring over 100 next-generation ASR-9 radars for major US. airports while relocating existing ASR-8s to secondary terminals. Thus within the next five years, almost every U.S. airport that supports commercial operations will be equipped with one of these sensitive, highly stable S-band radars. In view of their on- or near-airport location, rapid scan rate and direct data link to air traffic control personnel, it has been recognized that ASRs can also provide flight controllers with timely information on weather conditions that are hazardous to aircraft. An ASR's transmitted frequency, power, pulse-to-pulse stability and receiver sensitivity are well suited for weather sensing. Conversely, its broad elevation beamwidth, rapid antenna scan rate and non-uniform pulse transmission sequence introduce significant complications for the quantitative interpretation of echoes returned from weather. This paper reviews principal results of a four-year, FAA-sponsored program to evaluate the capabilities and limitations of ASRs for measuring storm severity.
Summary
Modern airport surveillance radars (ASR) are coherent, pulsed-Doppler radars used for detection and tracking of aircraft in terminal area air space. The Federal Aviation Agency (FAA is procuring over 100 next-generation ASR-9 radars for major US. airports while relocating existing ASR-8s to secondary terminals. Thus within the next five years...
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Advances in primary-radar technology
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 363-380.
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Summary
Current primary radars have difficulty detecting aircraft when ground clutter, rain, or birds interfere. To overcome such interference, the Moving Target Detector (MTD) uses adaptive digital signal and data processing techniques. MTD has provided the foundation for a new generation of primary radars called Airport Surveillance Radar-9 (ASR-9). In addition to achieving near-optimal target-detection performance, ASR-9 also provides timely weather information. The Federal Aviation Administration (FAA) is installing ASR- 9 systems at more than 100 airports across the United States.
Summary
Current primary radars have difficulty detecting aircraft when ground clutter, rain, or birds interfere. To overcome such interference, the Moving Target Detector (MTD) uses adaptive digital signal and data processing techniques. MTD has provided the foundation for a new generation of primary radars called Airport Surveillance Radar-9 (ASR-9). In addition...
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Electrical characteristics of microburst-producing storms in Denver
January 1, 1989
Conference Paper
Published in:
Proc. 24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 89-92.
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Summary
Coordinated Doppler radar and electrical measurements of thunderstorm microbursts were initiated by Lincoln Laboratory and the MIT Weather Radar group in Huntsville, AL in 1987. These measurements were intended to identify electrical precursors to aviation hazards at ground level and to study the relationship between the state of cloud convective development and the prevalent lightning type. The results of the Huntsville Study (Williams and Orville, 1988; Williamd et al., 1988) showed pronounced peaks in intracloud lightning activity and radar reflectivity above the melting level 5-10 minutes prior to maximum outflow velocities at the surface. A similar behavior has been reported by Goodman et al. (1988) for a thunderstorm observed in COHMEX in the same region. These observations support a prominent role for ice, both in promoting the intracloud lightning aloft and in subsequently driving the outflow by virtue of the melting process. All Huntsville cases studied were 'wet' microbursts with maximum low level reflectivity factors greater than 50 dBZ. The parent storms were deep (H>11km) and electrically active (flash rate greater than or equal to 1min^-1). Recent microburst studies in Denver (Hjelmfelt, 1987); Biron and isaminger, 1989) have identified, in addition to a majority of 'wet' microbursts, substantial numbers of dry microburst-producing storms (Z<10^3 mm^6/m^3) with elevated cloud bases and modest radar cloud tops. The present studies were aimed at determining to what extent the electrical manifestations observed in Huntsville were prevalent in Denver. This paper presents some preliminary results for the Denver measurements from the summer of 1988.
Summary
Coordinated Doppler radar and electrical measurements of thunderstorm microbursts were initiated by Lincoln Laboratory and the MIT Weather Radar group in Huntsville, AL in 1987. These measurements were intended to identify electrical precursors to aviation hazards at ground level and to study the relationship between the state of cloud convective...
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Multipath modeling for simulating the performance of the Microwave Landing System
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 459-474.
Summary
The Microwave Landing System (MLS) will be deployed throughout the world in the 1990s to provide precision guidance to aircraft for approach and landing at airports. At Lincoln Laboratory, we have developed a computer-based simulation that models the performance of MLS and takes into account the multipath effects of buildings, the surrounding terrain, and other aircraft in the vicinity. The simulation has provided useful information about the effects of multipath on MLS performance.
Summary
The Microwave Landing System (MLS) will be deployed throughout the world in the 1990s to provide precision guidance to aircraft for approach and landing at airports. At Lincoln Laboratory, we have developed a computer-based simulation that models the performance of MLS and takes into account the multipath effects of buildings...
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Wind shear detection with pencil-beam radars
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 483-510.
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Summary
Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of several organizations under contract to the Federal Aviation Administration, has been instrumental in the design and development of radar systems and automated weather-hazard recognition techniques for this application. The Terminal Doppler Weather Radar (TDWR) system uses automatic computer algorithms to ident* hazardous weather signatures. TDWR detects and warns aviation users about low-altitude wind shear hazards caused by microbursts and gust fronts. It also provides advance warning of the arrival of wind shifts at the airport complex. Extensive weather radar observations, obtained from a Lincoln-built transportable testbed radar system operated at several sites, have validated the TDWR system. As a result, the Federal Aviation Administration has issued a procurement contract for the installation of 47 TDWR radar systems around the country.
Summary
Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of...
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Wind shear detection with airport surveillance radars
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 511-526.
Summary
Airport surveillance radars (ASR) utilize a broad, cosecant-squared elevation beam pattern, rapid azimuthal antenna scanning, and coherent pulsed-Doppler processing to detect and track approaching and departing aircraft. These radars, because of location, rapid scan rate, and direct air traffic control (ATC) data link, can also provide flight controllers with timely information on weather conditions that are hazardous to aircraft. With an added processing channel, an upgraded ASR can automatically detect regions of low-altitude wind shear. This upgrade can provide wind shear warnings at airports where low traffic volume or infrequent thunderstorm activity precludes the deployment of a dedicated Terminal Doppler Weather Radar (TDWR). Field measurements and analysis conducted by Lincoln Laboratory indicate that the principal technical challenges for low-altitude wind shear detection with an ASR-groundclutter suppression, estimation of near-surface radial velocity, and automatic wind shear hazard recognition--can be successfully met for microbursts accompanied by rain at the surface.
Summary
Airport surveillance radars (ASR) utilize a broad, cosecant-squared elevation beam pattern, rapid azimuthal antenna scanning, and coherent pulsed-Doppler processing to detect and track approaching and departing aircraft. These radars, because of location, rapid scan rate, and direct air traffic control (ATC) data link, can also provide flight controllers with timely...
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Observability of microbursts using Doppler weather radar and surface anemometers during 1987 in Denver, CO
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-161
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for declaring a microburst from both Doppler radar and surface anemometer data are described. The main objective of this report is to compare the 1987 radar observed microbursts (which impacted the area covered by a surface anemometer system) with the surface mesonet observed microbursts. Of the 66 microbursts for which radar and mesonet data were available, 4 were not observed by the radar and 1 was not observed by the mesonet. All four microbursts not observed by the radar were classified as "dry" events with low surface reflectivities and with three of the four being relatively weak (peak velocity differences < 20 m/s) shear events. Possible reasons as to why these microbursts were not observed are discussed in detail. The strongest event exceeded 20 m/s (differential velocity) for two minutes and appears to have been missed due to a combination of very low reflectivity and a very shallow depth overflow.
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for...
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Observability of microbursts with Doppler weather radar during 1986 in Huntsville, AL
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-160
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were collected by both an S-band radar (FL-2) and C-band radar (UND). Surface data were collected by a network of 77 weather sensors covering an area of enarly 1000 square km centered approximately 15 km to the northwest of the FL-2 radar site. The UND site was located at the approximate center of the surface sensor network. A list of 131 microbursts which impacted the surface sensor network is presented. Particular emphasis is on the 107 events for which both radar data and surface data where available. Of these events, 14 were not observed by the surface network, while two events were not identified as microbursts by radar. Possible explanations of these missed microburst identifications are presented. The first case was an instance of the radar viewing a weak, asymmetric event from an unfavorable viewing angle. The second case describes an extremely shallow microburst outflow occurring at a heigh too low to be observed by the lowest elevation scan of the radar. In each of these cases, the featured microburst was very weak and, although a microburst-strength differential velocity was not observable by radar, in both instances the divergent wind pattern associated with the event was clearly evident in the radar velocity data field. All microbursts which exhibited a differential velocoity of in excess of 13 m/s were identified by radar. No microbursts went unobserved as the result of insufficient signal return.
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were...
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